Abstract

The outbreaks of highly pathogenic avian influenza (HPAI) in US poultry in 2014-15 were described by the US Department of Agriculture as the “worst animal disease outbreak in US history”, affecting over 48 million birds. In Australia, the market share for free-range eggs increased from 10% in 2000 to 50% in 2017, raising concerns about the impact of this change in farming methods on the risk of HPAI outbreaks. We use mathematical models as part of a collaborative project to assess the current risk of avian influenza outbreaks in the commercial Australian chicken industry, the potential impact of increasing free-range production, and the potential for intervention strategies to reduce this risk. Given high levels of biosecurity on current Australian free-range farms, increases in free-range farming practices are likely to result in a modest increase in HPAI outbreak risk. Current practices around water treatment are highly effective but there is scope to improve biosecurity around wild-bird access to sheds and feed storage areas. The short production cycle in chicken meat sheds limits the potential for HPAI outbreaks to occur in meat sheds, as depopulation and cleaning prevents long-term disease persistence. The combination of simulation and analytic methods enables a range of different scenarios to be considered, with findings helping to guide biosecurity policies.